There's something universal about thumb sucking: nearly all babies do it, and nearly all parents worry about it. While most such worries are unfounded, you should be concerned if your child sucks their thumb past age of 4 — late thumb sucking could skew bite development.

Young children suck their thumb because of the way they swallow. Babies move their tongues forward into the space between the two jaws, allowing them to form a seal around a nipple as they breast or bottle feed. Around age 4, this “infantile swallowing pattern” changes to an adult pattern where the tip of the tongue contacts the front roof of the mouth just behind the front teeth. At the same time their future bite is beginning to take shape.

In a normal bite the front teeth slightly overlap the bottom and leave no gap between the jaws when closed. Â But if thumb sucking continues well into school age, the constant pushing of the tongue through the opening in the jaws could alter the front teeth's position as they erupt. As a result they may not fully erupt or erupt too far forward. This could create an open bite, with a gap between the upper and lower teeth when the jaws are closed.

Of course, the best way to avoid this outcome is to encourage your child to stop thumb sucking before they turn four. If, however, they're already developing a poor bite (malocclusion), all is not lost — it can be treated.

It's important, though, not to wait: if you suspect a problem you should see an orthodontist for a full evaluation and accurate diagnosis. There are even some measures that could discourage thumb sucking and lessen the need for braces later. These include a tongue crib, a metal appliance placed behind the upper and lower incisors, or exercises to train the tongue and facial muscles to adopt an adult swallowing pattern. Often, a reward system for not sucking their thumbs helps achieve success as well.

Thumb-sucking shouldn't be a concern if you help your child stop before age 4 and keep an eye on their bite development. Doing those things will help ensure they'll have both healthy and straight teeth.